

<script>
const map=new WeakMap()
function visitCount(user){
  let count=map.get(user)||0
  count+=1
  map.set(user,count)
  return count
}
let user={name:'zhangsan'}
let user2={name:'lisi'}
console.log(visitCount(user)); //1
console.log(visitCount(user2)); //1
console.log(visitCount(user)); //2
user=null//引用计数：0，是可回收的状态


</script>